This invention relates to the field of combustion technology. More particularly, the invention relates to the design of a ramjet inlet and combustion chamber for a rotary ramjet engine, as well as to a method of operating such engines.
Over the years, aero-derivitive gas turbine engines have been successfully adapted for use in stationary power generation devices. However, improvements in overall cycle efficiency, necessary in order to reduce fuel cost, and reductions in complexity of generation devices, necessary in order to reduce maintenance costs, would still be desirable. Historically, various unconventional gas turbine designs have also been attempted. One such design was suggested by Campbell, in U.S. Pat. No. 3,557,551, issued Jan. 26, 1971, showing a gas turbine engine with rotating combustion chambers and high nozzle velocities. However, that device, like many others, did not adequately address the aerodynamic features necessary to reduce parasitic xe2x80x9c∫ PdAxe2x80x9d drag (i.e., aerodynamic pressure P acting over an exposed area A), or the friction drag of high speed rotating elements, to within tolerable limits in order to economically deploy such technology at higher (e.g., supersonic) inlet velocities.
Further, although there have been various attempts at developing an apparatus that incorporates the use of ramjet engines for the production of stationary power, most of such designs as taught by others have been practically incapable of operation at supersonic speeds, or were potentially capable of such operation only at low Mach numbers and with considerable aerodynamic drag losses. Even where the use of ramjets operating at supersonic speeds and employing the use of oblique shock wave compression were envisioned, such as in Price, U.S. Pat. No. 2,579,049, such devices were inherently inefficient for stationary power production, since such designs were based on axial flow devices, where the bulk of the flow field occurs along the shaft axis, rather than on a tangential flow device, where the bulk of the flow field and therefore the thrust is oriented tangential to the rim of a rotor.
To provide a ramjet engine realistically adapted to stationary power production, it is desirable, particularly in locales with strict environmental regulations, to provide a device in which undesirable combustion products are reduced. Thus, it would be desirable to provide a ramjet inlet, and more particularly, a supersonic ramjet inlet and the accompanying combustion chamber structure, that enables the engine to maintain high efficiency power output while reducing the generation of undesirable products of combustion (such as nitrogen oxides) or incomplete products of combustion (such as carbon monoxide).
Moreover, it is beneficial in such devices that parasitic drag be decreased, to increase overall efficiency, and thus decrease specific fuel consumption. Thus, it would be desirable that both the axial and the tangential fluid flow fields, at both the engine inlet and at the engine exhaust, as well as with respect to engine components located in the fluid flow path therebetween, be substantially matched such that, particularly at full load design conditions, the engine operates with high efficiency.
Depending upon the specific operating needs of a particular implementation, certain subsets of (or even all) of the foregoing can be implemented using various combinations of exemplary embodiments and aspects thereof described in the sections following.
One embodiment of a novel rotary ramjet engine design disclosed herein has a combustor configuration in which a flameholder is provided that extends toward the running clearance at a stationary, preferably substantially cylindrical tubular peripheral wall. This design preferably utilizes an inlet centerbody in which ramjet compression is achieved at supersonic inlet velocities, by exploiting an oblique shock extending from a leading edge structure laterally outwardly to, at the design velocity, confining inlet and outlet strakes. Preferably, the combustor and accompanying strakes are affixed to the rotor in a preselected, substantially matched helical angle orientation, so as to smoothly and continuously acquire clean inlet air and discharge the resulting products of combustion. The combustion chamber is simplified in that a rear wall of the inlet centerbody serves as a forward wall of a combustion chamber, providing for flame holding. By virtue of the rear wall of the inlet centerbody extending from the rim of the rotor outward to the cylindrical interior peripheral sidewall (less running clearance), a combustor cavity is defined to provide for thorough mixing of fuel and air, and to provide sufficient residence time for reaction of fuel with oxidant in order to minimize the escape of incomplete combustion products from the combustor.
The foregoing combustion chamber configuration provides for efficient mixing of fuel and air at supersonic inlet inflow velocities. As stated previously, this combustor flameholder extends outward from the rim of the rotor toward the stationary, substantially cylindrical tubular interior peripheral wall (less running clearance). In this manner, by the utilization of a rear wall of an inlet body, multiple shear layers are created, i.e., on both sides of the inlet centerbody, so that fuel/air mixing is improved. The shear layers lead to the creation of mixing vortices behind the rear wall of the inlet centerbody (i.e., within the flameholder), which provides for a more compact primary zone and for stable flameholding that is desirable at the design operational velocity. A still further feature is provided by an embodiment incorporating multiple inlet centerbodies, wherein multiple flameholders are utilized.
Further, it is to be understood that although a combustor cavity having roughly a segmented annulus shape and having a substantially rectangular cross-section at any selected station along the flow path is depicted, other designs utilizing an inlet body rear wall flameholder shape other than that just described are also possible (e.g, non-rectangular cross-sectional shape). However, by optimizing combustor volume, the xe2x80x9chot sectionxe2x80x9d components of the ramjet engine are reduced.
In another embodiment, a fuel/air mixture may be supplied at high velocity via inlet fluid compression ducts adjacent to the inlet centerbody, so that flashback from the combustor may be reliably avoided even in the case of fuels that have a very high flame velocity. Such a the high velocity inlet can also acoustically decouple the upstream fuel system acoustics from the combustion chamber acoustic perturbations. Thus, combustion may be more easily confined to the mixing zones behind the flameholder, i.e., the rear wall of the inlet centerbody.
Yet another aspect may involve matching the axial and tangential flows at the inlet inflow plane and at the exhaust outlet nozzle, providing a primarily tangential flow engine with reduced energy loss due to unmatched flow rates, or due to excess or unnecessary axial flow.